1. Field of the Invention
The invention relates to presses for hydrostatic extrusion with a die support and particularly to sealing such presses at the die end.
2. The Prior Art
In presses for hydrostatic extrusion, very high pressure levels are used; usually the working pressure is between 10 and 20 kbar. At this high pressure a reliable seal must be achieved between the inner wall of a press cylinder and a die or a die support and between the inner wall of the cylinder and a punch or a piston projecting into the cylinder, said punch or piston, when it is inserted into the cylinder, producing the high extrusion pressure in a pressure medium which is enclosed in a pressure chamber formed of the cylinder, the die and the piston. A billet to be extruded is located in the pressure chamber and is pressed out through the die under the effect of a pressure medium. On raising the pressure from atmospheric level to the extrusion level, the inner diameter of the cylinder increases by 0.5 to 1%, which requires a seal which is to prevent pressure medium from flowing out through a gap between the cylindrical wall and the piston and the die, respectively, which expands upon a pressure increase. Any leakage at the high pressures mentioned may involve severe damage to the die or the die support, which requires an exchange of these expensive parts. In U.S. Pat. No. 3,702,555 there is shown and described in more detail a press of the kind referred to in this invention. In Larker application Ser. No. 462,402, filed Apr. 19, 1974, and U.S. Pat. Nos. 3,865,387 and 3,877,707 there are shown different variations of high pressure seals for presses for hydrostatic extrusion, having a first sealing ring abutting the cylindrical wall and a seal holder and a second sealing ring sealing against a die or piston and a seal holder. These seals have meant a great improvement and have resulted in a great increase in the service life. However, certain drawbacks have remained.
Particular problems have been caused by the sealing ring, the inner surface of which seals against a die or a die support and the end surface of which seals against a seal holder, especially in the case of hot extrusion. In hot extrusion the die and the die support are heated by the billet which is heated up to 600.degree. C., and expand so that the contact force between these parts and the surrounding sealing ring becomes very high. When removing the die or support, cutting has been obtained. Any scratches occurring have meant that no sealing has been obtained in the subsequent pressing.